Charge indicating means for fluid pressure train brake systems



April 6, 1954 A. T. GORMAN 2,674,121

CHARGE INDICATING MEANS FOR FLUID PRESSURE TRAIN BRAKE SYSTEMS FiledJune 8, 1949 33 INVENTOR.

2 d* Andreu/Torman ATTORNEY Patented Apr. 6, 1954 CHARGE INDIGATINGMEANS' FOR FLUID "'PRESSURE'TRAIN BRAKE SYSTEMS Andrew, "L, Gorman,Pitcairn, o Ba.,. assigner to.

WestinghoixsclAiriBi-ake Company, a, corpora Application .Iune,8, 1949,lSerial No. 97,768

(Cl. 7k-e529)y 2.01aims. 11 This invention ,relates to iid ,pressurebrakes of the type employed on railwayftrainsfand more particularly toindicatingrmealls for use on the power car or locomotive forconstantlyinforming the operator or engineerofpltheconditioner the train withrespect Ato,pressurepoi fluid therein, or leakage oi fiuid underpressure therefrom, so that he may be governedaccordingly inkcontrolling the brakes on the traritobetter insure the safetyv 3 0thereof.

The onlymeansat presentenlployed on a rail- Way train to indicate totheoperatorthe pressure condition of the brake, pipe and brakeequ,igprnents ofthe train isa pressureigage-looatedin the eab` 15 onmodern locomotives havinghighcapacity,feedl valves andrbrake valveidevicesfor eiial'gfllthe brake pipe, Ysuch ior example, as .exemplifiedyin Patent 2,314,397, issued to., Ellis E. Hewitt on March 23, 1943,sincewith.suchlequiprnentithe brake pipe gage on the locomotivemayindicate@ that the brake pipeis fully chargedwhen `as a" lmatter of factthe pressure intihebrakeappieto the rear of the locomotive andparticularlynat the rear end of the train may 1loe-much lower.

Ii the engineer reliesuponthe.indication;by;` the pressure gagethat theb rake system. on` atrain is fully charged when,actuallyiullclrargeexists only inthe brake p-ipeat thelocomotiveand perhaps on a few oarsimmediately; 4adjacent `,the locomotive, it ispossible thatwhenhe:Qllll13.95., the brake valve devicetoeffeetangapplication-of braliesfa harsh,l damagingrunningin of'slack between cars will occur withpossible derailment of cars or buckling `of the train. Itisalso possiblethat an undesiresiemergency application `of the brakes will occurvlhenaservice application-isilitended if .the brake pipey gradient, that. is,the. difference between `the pressures .in the brake pipe at the irontand rear ofthe train, issuiiciently 50 many. mie withthebraketequipmentfemployed 25 the brakepipe@rassurent-thegeeleiirewillfle- 55 brake pipe and brake, equipments throughout thee 'x duce bythe tendencyI to equalizewith the lower Ypressure of fluid atthe rear ofthetrain and the consequent reduction in the pressure at the locolmotivemay result in an excessive service application of brakes or be at a ratesuilicient to effect an emergency application of brakes.

If an engineer should depend upon the brake pipe gage in cyclingoperationof train brakes duringdescent ofA agrade there alsoexists thepossibility of excessive service applications of brakes or of anundesired emergency application of brakes on the ltraindue to .reasonsabove mentioned, and there isalso the possibility that he may misjudgerecharging operations of the train to an extent that adequate control ofthe train is lost andthe train `may vrun away. More speciiically, inYcycling the brakes on a grade, it is customary to alternately apply thetrain brakes andltihen recharge the train brake system during which timethe brakes throughout the train will partially release. If the rechargeduring the intervals between applications is sufcient to provide anadequate reapplication oi' brakes through the train, the train safety isassured, but if inadequate,` as may occur particularly in ease oiexcessive leakage from the train brake system, the pressure of fluid inthe brake equipments toware'i the-rear of the train maygradually getlower and. lower until eventuallyv it. isinsufcient for the safety ofthe train. If the engineer senses such a condition he may eiect anemergency application of lbrakes on the train to bring it to a stop andthen, while holding the train stopped with the locomotive, recharge thesystem so as to be able to proceed with safety. Otherwise the train mayrun away. During such cycling operation the-brake pipe gage at thelocomotive may register full brake Vpipe pressure during rechargingopel'- ations while actually the pressure in the brake plpeand brakeequipments back of the locomotive may be gettinglower lower abovefinentioned.

In order to insure the safety oi a train it may loe-mentioned. here thatbefore a train ever moved by an engine or locomotive-the engineer makesa leakage test of the brake pip-e on the. train. To accomplish this herst charges the brake equipment on the train then makes a pa;- tialservice reduction in brake pipe pressure iollowed by movement oi thebrake valve device to lap position, in response to which, the brake conetrolling valve Idevices or the like on the cars oi' thel train alloperate to eiiect acorresponding serviceapplication ci brake and thenmove to their lap position. By observing the brake pipe gage on thelocomotive the engineer then measures the drop in brake pipe pressureover a certain period of time to see if the leakage is within prescribedlimits. If the leakage is excessive the cause must be found andcorrected before the engineer will move the train. With the brake valveand brake controlling valve devices on the locomotive and cars of thetrain in their lap position it will be observed however that this testis only of leakage of fluid under pressure from the brake pipe, whileleakage of fluid under pressure from both the brake pipe yand brakecontrolling valve devices in their release position might be muchgreater. Further, leakage will also vary with a train in motion andaccording to Whether the slack in the train is stretched or bunched. Theleakage test above mentioned is therefore only on the side of safety andwhile it provides the engineer with a general idea of the leakagecondition of the brake system of a standing train he -must neverthelessuse caution in subsequently braking the trahi to compensate forconditions which he is not aware of in order to avoid difficulties suchas above described.

Moreover with the very great tractive effort of modern locomotivescoupled with the modern high capacity feed valves and brake valvedevices to charge the brake pipe of a train, if the conductor of a trainoperates the usual conductors valve device at the rear end to cause aservice application of brakes, the engineer may never sense what isoccurring. He may note a slight slowing down or increased drag 4from.the train and since the brake pipe gage of the locomotive may stillindicate a fully charged brake pipe he may merely increase the output ofpower oi the locomotive to compensate and keepv the train moving orbreak it in two. Even in case o a break-in-two and an emergencyapplication of brakes throughout the train, the feed valve device mayrebuild brake pipe pressure at the locomotive to full lpressure withoutthe engineer sensing what has happened and therefore continue with fullpower of the locomotive until it is stalled if there lare sufficientcars still attached to the locomotive with their brakes applied. Ifthere are insuiiicient cars to stall the locomotive it may continuerolling for some time before the engineer becomes aware of thecondition.

From the above remarks it will therefore be seen that it is verydesirable that some means be provided the engineer to constantly informhim of the true condition of the brake pipe and brake equipments througha train with respect to pressure of fluid therein, or leakage of fluidunder pressure therefrom, so that at the time of initiating anapplication of brakes he may be governed accordingly, and for alsopositively drawing his attention to a condition such as created by abreak-in-two of a train or oi a conductor effecting a reduction in brakepipe pressure at the rear end of the train so that he will promptly outofi the power to the locomotive and permit the train to stop.

The principal object of the invention is therefore the provision ofimproved means for accomplishing the above results.

Other objects and advantages will become apparent from the followingmore detailed description of the invention.

In the accompanying drawing: Fig. l is a diagrammatic view, partly insection and partly in outline, of certain elements of a modernlocomotive brake equipment with which the invention is associated; andFig. 2 is a sectional view 4. of a portion of an indicating device shownin Fig. 1.

Description As shown in the drawing the reference numeral i designates alocomotive main reservoir adapted to receive and store iluid underpressure for controlling the brakes on the locomotive and cars of aconnected train; the reference numeral 2 designates a, brake pipeadapted to be connected to the brake pipe of a train in a Well-knownmanner;

reference numeral 3 designates an engineers automatic brake valve devicefor supplying fluid under pressure from said main reservoir to saidbrake pipe; and reference numeral i designates a feed valve' device forlimiting the pressure oi fluid thus supplied to the brake pipe to adegree predetermined by the adjustment of said feed valve device. Thebrake valve device il is of the general high capacity type employed onmodern locomotives and comprises a pedestal like body 5 to which isconnected the main reservoir i and upon which is removably mounted thefeed valve device Il. A cover element t secured to the top of the body 5has a chamber I containing the usual rotary valve 8 which is connectedby a shaft 9 to the usual handle i arranged to be operated to the usualbrake controlling positions that is, release, running, service, lap andemergency, by the engineer for controlling the brakes. in the drawingthe handle ISI and thereby the rotary valve 8 are shown in their runningposition which is employed for charging the brake system on thelocomotive and cars o1 a train.

The brake pipe 2 is open through a passage II in the brake valve body 5and a normally open brake pipe cut-off valve device I2 to a passage I3leading to the seat of the rotary valve The brake valve body also has afeed valve delivery passage I4 and a feed valve control passage I5 bothopen at one end to the seat of rotary valve 8 and at the opposite end tothe feed valve device 4. The main reservoir I is connected by way of apassage I6 to said feed valve device, With the rotary valve 8 in runningposition the one end of passage I4 opens through choke means such as arestricted port il in the side of said rotary valve to a cavity I8therein which cavity registers with passage I3, and a cavity I9 in saidrotary valve connects a branch 20 of passage i3 to passage I5.

The feed valve device 4 also is of the high capacity type employed onmodern locomotives and comprises a supply portion 2i for controllingcommunication between passages I5 and Ill and thereby supply of fluidunder pressure from the main reservoir I to the brake pipe 2 by way ofpassage I4, cavity IS in the rotary valve 3, passage I3, the cut-ofivalve device I2 and passage II. The feed valve device further comprisesa regulating portion 22 which controls the operation of the supplyportion 2i and the pressure of iiuid supplied thereby to the brake pipe.

The supply portion 2i of the feed valve device embodies a piston 23having at one side a control chamber 24 connected by Way of a passage 2tto a valve chamber 26 in the regulating portion 22. At the opposite sideof piston 23 is a valve cha-mber 21 which is open by way oi passage itwith the main reservoir I. A restricted passage 28 through piston 23connects chambers 2T and 24. Contained in valve chamber 2l' andconnected to a stem 29 of the piston 23 for movement with said piston isa valve 38 for controlling communication between the chamber 2'! and adelivery chamber 3I`which is open to passage I4 in the brake valve bodyaii'd'also by way of a passage v5 32 to a chamber33injthe-regulating1portion'22. A spring 34 contained in'haibeN-and-bearng at one end against' 'an' air Stiainer'i35'mounted' ona pistonguide- 35aac'ts on stern 29 for lconstantly urging the valve 30'to a closed position.

The regulating portion 22' 'of the feed valve device comprises a'movable vabutment 36 subject on one side to the lforceofap'ressureregulating spring 3l which is adjustable by the usualr hand Wheel 38. Attheopposite'side of abutment 36 is a control chamber -39 open to thelfeed valve control passage I5'in thefbrakevalvebody52 `-A valve 40contained in chamber 26' h as a uted stem slidably mountedin aboreprvidedthrough a bushing 4I secured in thefca'sirg".V 'The bushing4I extends through chamber 3'3'andtermin`ates" in chamber 39 in coaxial'relation-` tdthe'abutnient 36, said lbushing have a pluralityof radialbores connecting the bore therein to chamber ,33 vvhereby valve 4i! isadapted to control communication Ybetvve'en chambers 26 and 33.vvvProjecting from the end of the fluted stem'of the valve 40 fis'a pinlikestem 42 which slidably extends through ya suitable bore in one en'dof'bushing 40 into chamber 39 wherein 'it contacts abutment36. When thehand adjusted forcey of regulating spring 3l v on one side of abutment36 exceeds the opposing pressure of 'fluid in chamber'SB" said spring isadapted to open the valvef40 and When less said valve is adapted tobeclosed by' a spring 43.

According to the'invention I associate with the locomotive brakeequipment, so far described, an indicator device 44 which is adaptedtobe located in the cab of the locomotive for readyobservation bytheengineer.

The indicator device 44 comprises a casing containing Ytwocoaxiallyarranged and spaced apart movable abutments 45 and :'46,preferably in the form of bellows diaphragms, at the opposite or outersides of which there'are provided pressure chambers 4l and 4E,respectively, Whilethe adjacent sides of said abutments arevopen toatmosphere. Pressurev chamber 41 is open by way of a pipe 49 to the feedvalve delivery passage I4 in the body 5 of the brake valve device whilechamber 4S is open by way of a pipe y5Ilto passage II inthe brake valvedevice and thereby to the brake pipe 2. 'The two movable abutments 45and 46 are engaged on adjacent faces by oppositeends of a movable stem5I. Anr intermediate portion of the stem 5I is in the form of a toothedrackl 52 which is operative through a trainof gearsV 53 for adjusting apointer 54 with respect to'a dial 5e. Arranged to turn about thesameaxis and over the pointer 542 is a manually adjustable pointer 5e whichmay be carried by a crystal`51 mounted over the dial 55,` as indicatedin Fig. 2.

The pointer 54 has a @Normal Operating Range of movement over dial 55 tothe left of va line 5S and a Dangerous Operating Range of movement tothe right of said line. A light bias spring 59 provided' in chamber'48vacts on the abutment 4t for 'opposingfmovement of the pointer 54 in thedirection of line'58 at which line a second spring Bil,Y also containedin said chamber is arranged to become effective 4to oppose furthermovement of said pointerin the direction of the right hand.

A danger signaling device 6I, preferably of the audible electric bel1type, adapted 'to be located in the locomotive cab for Warning theengineer of the existence of a dangerous condition, has one terminalconnected withan electric lbattery 62 and its opposite terminalconnected to la xed contact te;anothernxedcontact'. Mibeingzconnectedto, the other terminal --of the battery.: 'memo Y well as `the brakeequipment thereon,r are ,leaktight and fully charged .to theadjustmentof the feed valve device 4. In. actual service such aleaktightbrakesystem is seldom Vif-ever obtained, but for the presentdescriptionlet it ybe assumedthat such is the rease,4 under whichconditionthere will be no flowv ofiiuidiunder pressure to the brake pipe2 andthe pressure of luidin said brake pipe will be effective throughpassages I I, i3, andZil in the brakeivalvev device, cavity I@ in therotaryvalve 8 andpassage. I5 -in chamber 3B of the regulating portioni22.of the feedvalve device 4, and deflect movable .abutment 5E againstspring 3l to permit valve 40 to close whereby pressure of fluid in`piston.chamberz'll .1x/vill beequalized through therestricted..passage'f28with the main reservoir pressure in Achamber?! topermit closing of valve 3i! by spring .34 .for preventing new of fluidunder` pressure to the .brake pipe. There being no flow ofiiuid. underpressure through the feed valve delivery passage I 4 to the brake pipeunder this vleaktight condition .the pressure of iiuidindiaphragmchamber 4i in the indicating device ,44 Wl11be=equal tobrakepipe pressure in chamber48, as .a result of which, .the spring 59 willactuate the;gear.trainxi53. to move the pointer 54 to the extreme leftside .of dial 55, in which position it is shown .in the drawingand whichindicates that therevis no .now :of .fluid under .pressurel to the brakesystemfand .that the 1 system is leaktight.

Nowassume that thereisacertain degree of leakage of fluid undervpressure fromtheibrake pipe 2.on the 'locomotive and connected cars of atrain .and from ther respective brake/equipments. Undersuch acondition-the pressure of iluid kin the brake pipe 2 and thereby in theconnected chamber .39 of the regulating portion 22 of the feed valvedevice will be reduced sufficiently belovv the opposing force .of .theregulat ing spring 3l to vpermit said spring Ato open valve 40 torelease iiuid :under pressure` from kpiston chamber 24 pastsaid valve tothefeed valve delivery passage I4 andthence to the brake pipe 2.vvherebymain reservoir rpressure in ,chamber 21 willactuate piston23, toopen thevalve ,3b to permit flow of fluid underpressurefromthe main reservoir Ito the delivers/,passage I4 and thence to the brake pipe2 and brakesystem of the train for increasing or maintaining. ithe, pressure of uidtherein.A The pressure ofV fluid in va brake pipe 2 will thus tend. tobuildup, and when'suinciently increased, such. pressure'acting inchamber 39v on movable abutme'nt`36A will -actuate said abutment againstspring` 3'I--to permit-valve 4l) to move toward its seat for restrictingflovv of fluidunder pressure from piston chamber 24vvith respect tosupply of fluid thereto through the restricted port T28 to sucha degreethat spring 34 vwill move the valvea to a posit'ionlwith re- Idilspectzyto. itsgsea't. Where the supDlM fof. ,-fiuidzito the brake pipe 2 willjust equal the leakage of fluid under pressure therefrom and from theconnected brake equipments of the train.

In case the leakage of fluid under pressure from the brake pipe 2 andconnected brake system of the train is of a greater degree the pressureof fluid in the brake pipe 2 at the locomotive and in chamber 39 of theregulating portion 22 will be reduced to a slightly lower degree, thanfor a lesser degree of brake pipe leakage, in which case the valve 40will be opened to a slightly greater extent followed by operation ofpiston 23 to effect a corresponding increase in opening of valve 30,whereby a greater amount of fluid under pressure will be supplied to thebrake pipe to offset the greater degree of leakage of fluid underpressure therefrom.

It will thus be seen that the movable abutment 35 and valve 4i! in theregulating portion 22 of the feed valve device will assume a positioncorresponding to the rate of leakage of fluid under pressure from thebrake pipe 2 and the brake system of a train and the piston 23 willoperate to correspondingly position the valve 35 with respect to itsseat to supply just suicient lluid to the brake pipe on the locomotiveto compensate for such leakage throughout the train. It will also beseen that if a conductors valve device at the rear of a train isoperated to effect a service reduction in pressure in the brake pipe onthe train and locomotive, or in case of a break-in-two back in thetrain, that the feed valve device 4 will operate to its capacity tosupply iluid to the brake pipe to compensate for such loss.

In order that the feed valve device 4 will restore and maintain pressureof fluid in the brake pipe as above described the control pressure inchamber 39 of the regulating portion 22 of the feed valve device istaken from passage II in the brake valve body and therefore is substantially equal to that in the brake pipe 2 on the locomotive, wherebythe feed valve device will operate at maximum capacity required torestore or maintain pressure of fluid in said brake pipe.

It will also be noted that the restricted port l1 in the side of therotary valve S will offer restriction to flow of fluid under pressurefrom the feed valve delivery passage I4 to passage I3 and thence to thebrake pipe, as a result of which, the pressure of fluid in said deliverypassage, when the feed valve device is operating, will exceed that inthe brake pipe on the locomotive. It has been found that the pressure offluid provided in the feed valve delivery passage I4 by operation of thefeed valve device will vary directly in proportion to the supply offluid under pressure required for maintaining the pressure of fluid in abrake system of a train against loss, as by leakage, by operation of aconductors valve device at the rear end of a train or even the partingof a train, and advantage is taken of this characteristic forcontrolling operation of the indicator device 44 to provide the engineerwith constant information with respect to the leakage condition of thetrain brake system, or loss of fluid under pressure therefrom byoperation of a conductors valve device or otherwise as above mentioned,in a manner which will now be described.

Since the pressure chamber 41 in the indicator device 44 is open to thefeed valve delivery passage I4 it will be apparent that the movableabutment 45 will be constantly acted upon by pressure ,offluld fromvsaidk passage which will vary/.according to loss of fluid under pressurefrom the brake system of a train, while the movable abutment 46 will beconstantly subject in chamber 48 to pressure of fluid in the brake pipe2 on the locomotive. If the brake system on the train is absolultelytight. as does not exist in service, then when the brake pipe is chargedto the adjustment of the feed valve device the pressure of fluid inchambers 4'I and 48 will be the same under which condition spring 59will actuate the abutments 46 and 45 and the gear train 53 to move thepointer 54 to its extreme left hand position, as above described.However in case the feed valve device 4 is operating to supply fluid tothe brake pipe at a rate corresponding to a certain rate of losstherefrom the pressure of fluid in the delivery passage I4 and therebyinchamber 41 of the indicator device 44 will exceed that in the brake pipeacting in diaphragm chamber 48 by a degree proportional to such loss,under which condition the movable abutments and 4B will be moved towardthe right hand against spring 59 until the pressure of said spring isincreased sufficiently to offset the greater pressure of fluid inchamber 4'I, whereby the pointer 54 will be moved to a correspondingposition on the dial 55. In case of greater leakage or loss of fluidunder pressure from the brake system on the train the pressure of fluidin the feed valve delivery passage I4 will be correspondingly higher andthe pointer 54 will assume a position further to the right on the dial55. For any permitted rate of leakage of fluid under pressure from thebrake system on a train the pointer 54 will thus assume a positionsomewhere between the extreme left hand position of dial 55 and the line`58, that is. within the Normal Operating Range.

When the engineer is making a leakage test on a train prior to leaving aterminal the hand or pointer 54 will therefore assume a position withrespect to dial 55 corresponding to the leakage of such fluid underpressure. The engineer will then position the pointer 55 over thepointer 54 and after the train is in motion any change in position ofthe pointer 54 relative to the pointer 55 will provide the engineer witha constant indication of any change in the leakage condition of thebrake system on the train so that when he desires to effect anapplication of brakes on the train he may be governed accordingly.

Since the pointer 54 assumes a position corresponding to the degree ofovercharge of the feed valve delivery passage I4 with respect to thepressure of uid in the brake pipe 2 on the locomotive, and therefore inaccord with the rate at which fluid under pressure is being supplied tothe train brake system, it will be apparent that when in releasing thebrakes during cycling operation the position of the pointer 54, relativeto the normal leakage condition of the brake system as indicated by thepointer 56, will provide an indication to the engineer of the degree ofcharge of the brake system toward the rear end of the train, since thelower the charge a greater amount of iluid under pressure will besupplied to the brake pipe than for a higher charge. Therefore, in casethe pressure of iluld in the brake system toward the rear of the traingradually diminishes during cycling operation, the pointer 54 will movefurther and further to the right to clearly indicate to the engineerthis condition so that he may act accordingly. The line 58 designateswhat may be considered the end of the safe operating range of pointer 54with respect to loss of fluid under pressure from the brake system andmovement of said pointer to the opposite side of said line will indicatevisually that such loss is becoming dangerous with respect to safecontrol of the train. The movable contact 65 may be arranged to engagethe contacts E3, 65 to cause operation of the bell 6l at any time afterthe pointer 54 moves to the right of line 58, if desired, but I preferthat the bell 6| only operate in case of loss of iiuid from the brakesystem such as may be occasioned by pulling a train in two in which casethe rate of supply of fluid to the brake pipe will be such as to throwthe pointer 54 to substantially its extreme right hand positionwhereupon the bell 6I will operate to call the engineers attentionaudibly to this condition.

Movement of the pointer 54 from line 58 to its extreme right handposition will be opposed by the auxiliary spring 59 the only purpose ofwhich however is to shorten the movement of the pointer 54 for such anabnormal condition whereas greater movement of the pointer is requiredin the normal operating range thereof to the left of line 58 to providewith a desired degree of accuracy,

the information required by the engineer in connection with normal lossof iiuid under pressure from the brake system.

Summary From the above description it will now be seen that I haveprovided an arrangement for use with modern locomotive brake equipmentwhich will provide the engineer on the locomotive with a constantindication of the leakage condition of his train or of the loss of fluidunder pressure therefrom, so that he may control the brakes thereonaccordingly with a maximum safety to the train and to laden carriedthereby.

Having now described the invention, what I claim as new and desire tosecure by Letters Patent, is:

1. In an automatic air brake system, in combination, a source of fluidunder pressure, a brake pipe, a feed valve device comprising a supplyportion for supplying fluid under pressure to said brake pipe, anengineers brake valve device for establishing communication throughwhich lluid under pressure supplied by said supply portion ilows to saidbrake pipe and including choke means in said communication of less 110Wcapacity than said supply portion, said feed valve device furthercomprising a regulating portion subject to pressure in saidcommunication at the brake pipe side of said choke means and operativeto control said supply portion to limit pressure of fluid in said brakepipe, spring means, pressure sensitive means subject to pressure offluid supplied by said supply portion at one side of said choke meansacting in opposition to pressure of said spring means plus pressure offluid in said brake pipe at the opposite side of said choke means andmovable in accordance with the differential between such opposing iiuidpressures, a dial for indicating differential between pressures of fluidin said communication at opposite sides of said choke means, and anindicating element connected to and actuated by said pressure sensitivemeans relative to said dial.

2. In an automatic air brake system, in combination, a source of uidunder pressure, a brake pipe, a feed valve device comprising a supplyportion for supplying fluid under pressure to said brake pipe, anengineer-s brake valve device for establishing communication throughwhich fluid under pressure supplied by said supply portion flows to saidbrake pipe and including choke means in said communication of less iioWcapacity than said supply portion, said feed valve device furthercomprising a regulating portion subject to pressure in saidcommunication at the brake pipe side of said choke means and operativeto control said supply portion to limit pressure of fluid in said brakepipe, and an indicating device comprising a dial graduated forindicating differential between pressures of iiuid in said communicationat opposite sides of said choke means, a pointer adjustable manuallyover said dial, spring means, pressure sensitive means subject topressure of iiuid supplied by said supply portion at one side of saidchoke means acting in opposition to pressure of said spring means pluspressure of uid in said brake pipe at the opposite side of said chokemeans and movable in accordance with the diiierential between suchopposing uid pressures, and another pointer actuated by said pressuresensitive means over said dial.

References Cited in the le of this patent UNITED STATES PATENTS GreatBritain Nov. 27, 1919

